1. Field of the Invention
The present invention relates to a thermal head for applying thermal activation energy to a thermally active sheet including a thermally active component; a thermal activation device employing the thermal head; and a printer assembly employing the thermal activation device. More particularly, the invention relates to a technique for preventing the activated thermally active component from being adhered to the thermal head.
2. Description of the Related Art
In recent years, a thermally active sheet (a print medium containing a thermally active component in a top coat surface thereof and exemplified by a heat-sensitive self-adhesive label) has been known as a kind of labels affixed to products. The thermally active sheets have found a wide range of applications such as POS labels affixed to food products, affixing labels used in physical distribution/delivery, labels affixed to medical products, baggage tugs, indication labels affixed to bottles or cans and the like.
The heat-sensitive self-adhesive label includes a sheet-like label substrate (such as a base paper); a heat-sensitive adhesive layer formed on a back side of the substrate and containing a thermally active component which is normally non-adhesive but develops adhesiveness when heated; and a printable surface formed on a front side of the substrate.
The heat-sensitive adhesive includes a thermoplastic resin, a solid plasticizer and the like as the major components thereof, and has a nature that the heat-sensitive adhesive is non-adhesive at normal temperatures but is activated to develop the adhesiveness when heated by the thermal activation device. Normally, activation temperatures are in the range of 50 to 150xc2x0 C., in which range the solid plasticizer in the heat-sensitive adhesive is molten to impart the adhesiveness to the thermoplastic resin. The molten solid plasticizer is gradually crystallized via a supercooled phase so that the adhesiveness is maintained for a given period of time. While the heat-sensitive adhesive exhibits the adhesiveness, the label is affixed to an object such as a glass bottle or the like.
The printable surface of the heat-sensitive self-adhesive label is comprised of, for example, a heat-sensitive color-developing layer containing a kind of thermally active component. The heat-sensitive self-adhesive label is subjected to a thermal printer assembly equipped with a common thermal head for printing a desired character(s) or image on the printable surface thereof and thereafter, subjected to the thermal activation device for activation of the heat-sensitive adhesive layer thereof.
On the other hand, a printer assembly is now under development, which incorporates therein the thermal activation device for sequentially conducting thermal printing on the heat-sensitive self-adhesive label and activation of the heat-sensitive adhesive layer thereof.
Such a printer assembly has an arrangement as shown in FIG. 9, for example.
Referring to FIG. 9, a reference sign P2 represents a thermal printer unit, a sign C2 represents a cutter unit, a sign A2 represents a thermal activation unit, and a sign R represents a heat-sensitive self-adhesive label wound into a roll.
The thermal printer unit P2 includes a printing thermal head 100, a platen roller 101 pressed against the printing thermal head 100, and an unillustrated drive system (including an electric motor, and gear array, for example) for rotating the platen roller 101.
As seen in FIG. 9, the platen roller 101 is rotated in a direction D1 (clockwise) there by paying out the heat-sensitive self-adhesive label R, which, in turn, is subjected to thermal printing and then discharged in a direction D2 (rightward).
The platen roller 101 further includes unillustrated pressure means (such as a helical spring or plate spring), a resilient force of which acts to bias the platen roller 101 surface against the thermal head 100. Thus, the platen roller also operates as pressure means for pressing the heat-sensitive self-adhesive label R.
The printer unit P2 shown in FIG. 9 operates the printing thermal head 100 and platen roller 101 based on a print signal from an unillustrated print control unit, thereby accomplishing desired printing on a thermal coat layer 501 of the heat-sensitive self-adhesive label R.
The cutter unit C2 serves to cut the heat-sensitive self-adhesive label R, thermally printed by the thermal printer unit P2, in a proper length. The cutter unit includes a movable blade 200 operated by a drive source (not shown) such as an electric motor, and a fixed blade 201. The movable blade 200 is operated at a predetermined timing under control of the unillustrated control unit.
The thermal activation unit A2 includes an insertion roller 300 and a discharge roller 301 rotated by, for example, an unillustrated drive source for inserting and discharging the cut heat-sensitive self-adhesive label R; and a thermally-activating thermal head 400 and a platen roller 401 pressed against the thermally-activating thermal head 400, which are interposed between the insertion roller 300 and the discharge roller 301. The platen roller 401 includes an unillustrated drive system (an electric motor and gear array, for example), which rotates the platen roller 401 in a direction D4 (a counterclockwise direction as seen in FIG. 9) so that the heat-sensitive self-adhesive label R is conveyed in a direction D6 (a rightward direction as seen in FIG. 9) by the insertion roller 300 and discharge roller 301 rotated in respective directions D3 and D5. On the other hand, the platen roller 401 includes unillustrated pressure means (such as a helical spring or plate spring), a resilient force of which acts to bias the platen roller 401 surface against the thermally-activating thermal head 400.
A reference sign S represents a discharge detection sensor for detecting the discharge of a heat-sensitive self-adhesive label R. The printing, conveyance and thermal activation of the subsequent heat-sensitive self-adhesive label R are performed in response to the discharge detection sensor S detecting the discharged heat-sensitive self-adhesive label R.
The thermally-activating thermal head 400 has an arrangement as shown in FIG. 11, for example.
Referring to FIG. 11, a reference sign 600 represents a ceramic substrate as a heat releasing substrate. A glaze layer 601 as a heat storage layer is overlaid on the overall surface of the ceramic substrate 600 in a thickness on the order of say 60 xcexcm. The glaze layer 601 is formed by, for example, printing a glass paste on the substrate followed by baking the paste at predetermined temperatures (e.g., about 1300 to 1500xc2x0 C.).
A heat generating resistance 602, such as of Taxe2x80x94SiO2, is formed on the glaze layer 601 by laminating a Taxe2x80x94SiO2 layer thereon by sputtering and processing the resultant layer into a predetermined pattern by a photolithography technique.
Also formed on the glaze layer 601 is an IC portion 605 for controlling power supply to the heat generating resistance 602. A sealing portion 606, such as of a resin, is overlaid on the IC portion for protection.
On the heat generating resistance 602, an electrode 603 is formed by laminating a layer of Al, Cu, Au or the like by sputtering in a thickness of about 2 xcexcm and processing the resultant layer into a predetermined pattern by the photolithography technique. Power is supplied to the heat generating resistance 602 via the electrode 603 under control of the IC portion 605.
On the electrode 603 and heat generating resistance 602, a protective layer 604 of hard ceramics such as Sixe2x80x94Oxe2x80x94N or Sixe2x80x94Alxe2x80x94Oxe2x80x94N is laminated by sputtering for preventing the oxidization and wear of the electrode 603 and heat generating resistance 602.
The thermally-activating thermal head 400 of the above arrangement and the platen roller 401 are operated at a predetermined timing under control of the unillustrated control unit. The heat-sensitive self-adhesive label R having the heat-sensitive color developing layer 501, a colored print layer 502 and a thermally-active adhesive layer K, as shown in FIG. 10, is activated at the thermally-active adhesive layer K by heat generated by energizing the thermally-activating thermal head 400, so that an adhesive force is developed.
After the adhesive force of the heat-sensitive self-adhesive label R is developed by the thermal printer unit P2 thus arranged, an indication label, price label or advertisement label may be affixed to glass bottles containing liquors or medical agents or to plastic containers. This negates the need for a separation sheet (liner) provided at the adhesive label sheet commonly used in the art, providing a merit of cost reduction. In addition, the invention provides further merits in terms of resource savings and environmental problems because the separation sheets producing wastes after use are not required.
However, the conventional thermal activation unit A2 for heat-sensitive self-adhesive label R encounters a problem that the heat-sensitive adhesive and substances transformed therefrom (chemically changed or carbonized substances by heat) are adhered to the surface (protective layer 604) of the thermal head 400.
Specifically, as shown in FIG. 12A, the platen roller 401 is constantly pressed against the surface of the protective layer 604 of the thermal head 400. When the heat-sensitive self-adhesive label R cut in the predetermined length by the cutter unit C2 is inserted between the platen roller 401 and the protective layer 604, the thermally-active adhesive layer K is heated by the heat generating resistance 602 of the thermally-activating thermal head 400 to form a dwelling molten mass K1 of thermally active adhesive.
The most of the molten mass K1 adheres to individual surfaces of the thermally-active adhesive layers K of the heat-sensitive self-adhesive labels R delivered one after another, and is discharged along the movement of the heat-sensitive self-adhesive labels R. The discharged molten mass K1 is allowed to cool to form a solid mass on the protective layer 604. The solid mass gradually accumulates to form a fixed mass G1.
The fixed mass G1 thus formed interferes with the movement of the heat-sensitive self-adhesive label R, so that the molten mass K1 of the thermally active adhesive cannot be discharged from space between the protective layer 604 and the platen roller 401.
While dwelling at place between the protective layer 604 and the platen roller 401, the molten mass K1 of the thermally active adhesive is subject to thermal energy for a relatively long period of time, whereby the thermally activated adhesive is transformed into chemically changed or carbonized substances which are rigidly fixed to a surface portion of the protective layer 604 directly above the heat generating resistance 602 (in a scorchedly fixed state, for instance). In such a scorchedly fixed state, thermal conductivity from the heat generating resistance 602 to the thermally-active adhesive layer K of the heat-sensitive self-adhesive label R is decreased, resulting in a drawback of lowered cohesive strength of the heat-sensitive self-adhesive label R.
In order to ensure that the thermal activation unit A2 positively heats a leading and a trailing portion of the thermally-active adhesive layer K of the heat-sensitive self-adhesive label R, the control is provided such that power supply to the heat generating resistance 602 is started a few moments before the arrival of the leading portion and is continued for a few moments after the passage of the trailing portion. This produces some period of time during which the heat-sensitive self-adhesive label R is absent at place between the protective layer 604 and the platen roller 401. In this state, therefore, the platen roller 401 is at idle as contacting the protective layer 604. This leads to a problem that the molten mass K1 of the thermally active adhesive on the protective layer 604 adheres to a periphery of the idling platen roller 401 (refer to a sign G2 in FIG. 12B).
Furthermore, there may be a case where the thermally-active adhesive masses G2 on the periphery of the platen roller 401 are repeatedly heated by the heat generating resistance 602 so as to be transformed into chemically changed or carbonized substances, which are rigidly fixed to the periphery of the platen roller 401.
In another case, the thermally-active adhesive masses G2 on the periphery of the platen roller 401 are molten by repeated heating by the heat generating resistance 602, thus exhibiting a strong adhesive force. Accordingly, some of the adhesive masses G2 are adhered to a front surface of the subsequent heat-sensitive self-adhesive label R, contaminating the printable surface thereof.
Furthermore, there exists a problem that the peripheral surface of the platen roller 401 is deteriorated in smoothness due to the adherence of multiple thermally-active adhesive masses G2 and hence, the subsequent heat-sensitive self-adhesive label R cannot be uniformly heated, thus failing to exhibit a sufficient adhesive force.
In still another problem, some of the thermally-active adhesive masses G2 on the periphery of the platen roller 401 are re-adhered to the protective layer 604 on a side where the heat-sensitive self-adhesive label R is inserted, thus forming a deposition G3 thereon. The deposition G3 is gradually accumulated to a degree that the insertion of the subsequent heat-sensitive self-adhesive label R is blocked.
The insertion failure of the heat-sensitive self-adhesive label R associated with the deposition G3 results in a long idling of the platen roller 401. This increases load on a drive motor for the platen roller 401, accelerating the deterioration of the motor. Furthermore, since the heat from the heat generating resistance 602 is not absorbed by the heat-sensitive self-adhesive label R, thermal load is increased to shorten the service life of the heat generating resistance 602.
The aforementioned problems are encountered not only by the thermal head of the thermal activation unit but also by the printing thermal head 100.
The invention has been contrived to solve the above problems and has an object to provide a thermal head capable of preventing the adherence of a thermally active component, a thermal activation device for thermally active sheet employing the thermal head, and a printer assembly employing the thermal activation device.
For achieving the above objects, a thermal head (H) according to the invention comprises a heat storage layer (glaze layer 2) formed on a heat releasing substrate (ceramic substrate 1), a plurality of heat generating resistances (3) and electrodes (4a, 4b) for power supply to the individual heat generating resistances formed on the heat storage layer thereby forming an array of heat generating elements, and a protective layer (7) covering the top surfaces of these parts; and applies thermal activation energy to a print medium (heat-sensitive self-adhesive label R) including a thermally active component by supplying power to the heat-generating element array; the thermal head characterized in that two substantially parallel lines of anti-adherence layers against thermally-active-component (8a, 8b) are formed on the protective layer as sandwiching a protective layer portion directly above the heat-generating element array.
Thus, the thermally active component activated by receiving the thermal energy from the heat-generating element array is discharged from the portion directly above the heat-generating element array onto the anti-adherence layer against thermally-active-component so as to be prevented from forming the deposition. Accordingly, the problem associated with the thermally active component dwelling on the portion directly above the heat-generating element array can be obviated. This, therefore, prevents the scorched fixing of the thermally active component onto the protective layer, which is encountered in the prior art. Hence, the drawback of decreased thermal conductivity to the print medium including the thermally active component can be avoided.
Further, the anti-adherence layer against thermally-active-component may comprise a resin layer of low surface energy. Thus, the adherence of the thermally active component is effectively prevented by the resin layer of low surface energy which exhibits, for example, water or oil repellency. Further, the resin layer of low surface energy may have a pencil hardness in the range of 2 B to 5 B. This provides a more effective prevention of the adherence of the thermally active component because whenever the print medium including the thermally active component is inserted between the thermal head and the platen roller, the print medium contacts the resin layer to polish the surface of the resin layer, thereby constantly exposing a new surface of the resin layer.
Further, the resin layer of low surface energy may comprise a silicone resin or fluorine resin. This leads to an easy formation of the resin layer of low surface energy.
Further, the resin layer of low surface energy may comprise a fluorine resin layer containing a minor amount of powder of Si-based, Ti-based or Ta-based oxide or nitride film or complex film of these compounds. This leads to a resin layer featuring high water or oil repellency and enhanced film strength.
Further, the resin layer of low surface energy may comprise a fluorine resin containing a minor amount of metal element or carbon. This leads to the formation of a resin layer featuring high water or oil repellency, conductivity and resistance to electrostatic destruction.
Further, the anti-adherence layer against thermally-active-component may be composed to satisfy a relation Txe2x89xa6W/100 where T denotes a thickness of the anti-adherence layer against thermally-active-component, and W denotes a gap between two lines of anti-adherence layers against thermally-active-component. This ensures adequate surface contact between the anti-adherence layer against thermally-active-component and the print medium such that the surface of the resin layer is efficiently polished for more effective prevention of the adherence of the thermally active component.
Further, the two lines of anti-adherence layers against thermally-active-component may be tapered at opposite faces thereof. This provides an increased contact surface between the anti-adherence layer against thermally-active-component and the print medium such that the surface of the resin layer is efficiently polished for more effective prevention of the adherence of the thermally active component.
Further, in a case where the heat-generating element array has a convex or mesa-like section, the anti-adherence layer against thermally-active-component may be formed in a manner that a top surface of the anti-adherence layer is lower than a surface directly above the heat-generating element array. This permits the use of a simple procedure for forming the anti-adherence layer against thermally-active-component, negating the need for film thickness control taken when the anti-adherence layer against thermally-active-component is formed by coating a liquid material.
Further, the anti-adherence layer against thermally-active-component may be formed by applying a liquid resin material onto the protective layer. Thus, the anti-adherence layer against thermally-active-component can be readily formed from the liquid resin material by, for example, screen printing, dip coating, spray coating, brush coating or the like.
Further, the anti-adherence layer against thermally-active-component may be affixed to the protective layer via an adhesive layer. This provides a mode wherein a sheet-like body previously formed with the anti-adherence layer against thermally-active-component is provided with the adhesive layer at a back side thereof, such that the anti-adherence layer against thermally-active-component may be readily mounted to place by affixing the sheet-like body. This also facilitates the replacement of the anti-adherence layer against thermally-active-component when the anti-adherence layer is worn or damaged.
A thermal activation device for thermally active sheet according to another aspect of the invention at least comprises activating heating means for activating by heating a thermally active layer of a thermally active sheet formed with the thermally active layer at least on one side of a sheet-like substrate thereof; conveyance means for conveying the thermally active sheet in a predetermined direction; and pressure means for pressing the thermally active sheet against the activating heating means, the device characterized in that the above thermal head is employed as the activating heating means.
This ensures that the adherence of the thermally active component to the thermal head is effectively prevented and hence, the thermal activation device for thermally active sheet featuring high thermal conductivity to the print medium is provided.
A printer assembly according to another aspect of the invention comprises the above thermal activation device for thermally active sheet. Thus is provided the printer assembly always capable of thermally activating the printed print medium with good thermal conductivity.
Further, the printer assembly is characterized in that the thermally active sheet may be formed with a heat-sensitive color developing layer, and that the above thermal head may be employed as thermal activation means for the heat-sensitive color developing layer. This ensures that the print medium is always thermally activated with good thermal conductivity while a component of the heat-sensitive color developing layer is prevented from adhering to the surface of the thermal head. Hence, favorable printing results can be obtained.